This invention relates to improved bearing assemblies, and more particularly, to an improved bearing unit especially useful as a trolley wheel for overhead conveyors and an improved inner race structure for that bearing unit.
In general, two types of ball bearing assemblies are available, namely, full-ball complement and retainer-type structures. Retainer-type assemblies typically include an outer race, a single piece inner race, a lesser number of balls between the two races than in a full-ball complement assembly, and a retainer or cage at least partially enclosing the balls but not engaging either race for retaining the balls in the assembly. Retainer-type assemblies are generally used to handle lighter loads but are capable of attaining higher speeds principally due to the lesser number of balls and the resulting lower friction produced in the assembly due to the elimination of ball-to-ball contact.
In full-ball complement bearing assemblies, a series of balls is fitted between a multipart inner or outer race, or a single piece inner or outer race including a filling slot, and a single piece opposing race to enable insertion of the balls into the assembly.
One type of full-ball complement bearing assembly includes a two part inner race having two, symmetrical, machined, annular inner race parts including a curved raceway. The inner race dividing line is directly under or in line with the ball centers. The two parts are held together by a flanged hub or sleeve which is passed through both parts, expanded or riveted over at the end opposite the flanged portion. In this form each of the inner race parts essentially bears an equal load.
Another full-ball complement bearing unit is shown in French Pat. No. 502,354 and includes a two part inner race assembly where both parts appear to be fully machined and one includes a wider portion of the ball track than the other. In this unit the outer race must be heated and expanded to allow insertion of the ball members between the races.
Other types of multipart inner race bearing assemblies have a single, machined, annular inner ring and a flat washer or flat snap ring substituted for a missing raceway shoulder to retain the balls in the unit after assembly. This type assembly suffers from several drawbacks including excessive end play or axial runout which causes the bearing assembly to skew or improperly track, excessive wear on the balls due to a gap in and a lack of contour of the support surface for the balls and ball engagement with the sharp corner of the snap ring or washer in certain circumstances, and excessive stress on the balls because of the inclusion of a cylindrical or "flat" raceway portion in the raceway area which provides principal load support which is not contoured to the shape of the ball.
In order to avoid the above-noted additional processing steps for expanding the races to allow assembly, as well as the above functional problems, it has previously been necessary to utilize an inner race assembly having two machined inner race parts which provide a wide opening for ball insertion, neither of which parts provides the majority of the support and ball retention functions. Of course, such assemblies are significantly more expensive to manufacture than the present invention. The present invention is designed as a less expensive, full-ball complement trolley wheel or bearing assembly which can be assembled in its ambient state, is competitive from a price standpoint with retainer type wheels, and which, even in the partially machined preferred embodiment, includes the performance characteristics of more expensive, fully machined, full-ball complement wheels.